Problem
Calculate approximate theoretical draft in mm of water for a 40 m chimney when outside air density is 1.20 kg/m³ and average flue-gas density is 0.85 kg/m³.
Given Data
Write all quantities in consistent SI units before substitution.
Formula and Solution
Pressure difference = gH(ρa−ρg)=9.81×40×0.35=137.34 Pa. Since 1 mm water ≈9.80665 Pa, draft = 14.0 mm water.
Engineering Check
Check units, magnitude and physical meaning. State any simplifying assumptions and avoid mixing mass flow per hour with energy per second.
Practice Variation
Repeat the problem after changing one input by 10% and explain how the answer responds.